It is quite common for storing and shipping of perishable products such as fruits, vegetables and the like, to provide refrigeration and/or controlled atmospheres to maintain the freshness of the perishable goods. Particularly, because many perishable goods such as tropical fruits and the like must be shipped relatively long distances to remote markets, it is difficult to maintain the freshness of these goods after harvest during the sometimes extended time periods required for shipping, importation, and distribution. Moreover, for most of these products, it is desired to avoid freezing the products, which can cause extensive damage and deterioration to the quality and desirability of the product.
It is also well known that certain perishable products such as fruits or vegetables can be maintained in fresher condition at above-freezing refrigerated temperatures, especially when maintained in an atmosphere which is less conducive to rapid ripening and spoilage. For example, U.S. Pat. No. 4,716,739, which issued to S. Harris et al., describes a system wherein a container loaded with perishable products is initially flushed with a nitrogen gas to reduce the oxygen level to a base initial level, and thereafter oxygen levels are controlled by selective inflow of ambient air. The carbon dioxide levels (CO.sub.2) are maintained below a predetermined maximum by the use of a CO.sub.2 scrubber device. In the Harris system, however, the seal of the container is critical, as it must be leak tight to a sufficient degree to control the inflow of oxygen, but cannot be completely air-tight, as inflowing ambient air is relied upon to provide a certain minimum oxygen level.
It is also known that fruit and other perishable items continue what is known as "respiration", utilizing oxygen and giving off CO.sub.2, after harvesting. The rate of respiration can fluctuate widely, and is affected greatly by temperatures and oxygen levels in the atmosphere around the products. The Harris patent also refers to previous patents, such as U.S. Pat. No. 3,239,360, which presumably teach the requirement of periodically purging the atmosphere with nitrogen gas based upon controls within the container which respond to oxygen levels within the shipping container itself. Such arrangements, however, were based solely on the oxygen level within the container and required containers designed to allow leakage of gas. These systems also would require relatively large amount of nitrogen for long shipping distances.
A similar prior technology is discussed in the Harris patent, and referred to as the "TECTROL" System associated with the Transfresh Corporation. The container in this system would be sealed prior to shipping and prior to being precharged with a controlled atmosphere gas. During shipping, the oxygen and carbon dioxide levels within the container were to be controlled merely by a bleed hole which enabled the inflow of ambient oxygen, and the inclusion of hydrated lime within the container to absorb excessive amounts of carbon dioxide. In such a situation, it is virtually impossible to adequately maintain the atmospheric conditions within the container throughout the shipping and storage procedures.
Another fresh food storing device is set forth in U.S. Pat. No. 4,961,322, and includes both a cooling mechanism and a supply of nitrogen. Oxygen levels within this device are to be controlled by the input of nitrogen and/or the use of a lighting lamp therewithin to encourage photosynthesis. Yoguma et al. patent also contemplates the use of a two-way pressure regulating means and a safety valve to ensure that pressure within the container does not exceed a predetermined level, and a discharge hole of the pressure regulating means which is to enable the drainage of water collected in the bottom of the storing volume. This device, however, is not practical for shipping large quantities of perishable goods over long distances.
Other prior art references, such as U.S. Pat. No. 4,454,723 (which issued to G. Weasel) also recognized the desirability of providing controlled atmoshere to refrigerated produce transport devices. Particularly, the Weasel reference sets forth a desirable oxygen level of between about 1 and 5%. Similarly, U.S. Pat. No. 5,172,558 (which issued to R. Wassibauer et al.) suggests the control of oxygen, carbon dioxide, ethylene and argon gases within the storage volume of a refrigerated container by the use of initial nitrogen flushing, and, thereafter, the addition of ambient air to ensure minimal levels of oxygen, and the addition of other gases provided in the form of special containers with the device as needed. Other systems, such as may be found in cargo ships or the like, may include a nitrogen generator which provides inert gas to large cargo hold areas in which produce containers are maintained for shipping. Such arrangements, however, do not provide controlled atmosphere to individual containers, and rely on bulk handling of the potentially widely varying conditions within such containers.
As with many of the other prior devices and procedures heretofore available, this art suggests arrangements and assemblies which require relatively substantial structures and support equipment. Heretofore, there has not been available a single integral yet flexible controlled atmosphere container system which can reliably provide optimal provision of controlled atmospheric conditions within a plurality of individual and transportable containers for perishable products in a substantially uniform and predictable manner.